A conventional mobile system for crime and disaster prevention, utilizing a battery as a single power source, consumes lots of power in a short: time period because it performs complex functions, including a motor driving function and a gas leak sensing function. When a battery is used as a power source for this kind of mobile system, it is impossible to use the battery continuously for a long time period due to its limited capacity. Further, when a normal operation (e.g., when all the functions are performed) is executed, the battery voltage decreases drastically, until operation of the mobile system is completely stopped and the desired functions are not performed. Thus, in previous systems, to use the mobile system for a long period of time, it was necessary to use a battery having a large capacity. However, batteries having sufficient capacity are undesirably large and heavy.